The podocyte is a highly specialized epithelial cell that forms multiple foot processes along the glomerular capillary basement membrane. The "junction" between foot processes (slit diaphragm) is critical to selective glomerular permeability. Podocyte injury is a hallmark of glomerular disease and is prominent early in the course of diabetic nephropathy and other causes of chronic kidney disease. Loss of slit diaphragms results in altered glomerular hemodynamics, proteinuria and progressive renal failure. The slit diaphragm shares many features of typical epithelial cell junctions, yet little is known about how these structures are regulated. Based upon our work in MDCK cells, we hypothesize that G proteins are likely to be critical molecules for regulating slit diaphragm structure/function. Ga12 through interactions with ZO-1 is likely to regulate Rho and/or Src pathways and the actin cytoskeleton in podocytes. In Aim 1, the interaction of ZO-1 and Ga12 will be studied in mouse glomeruli and cultured podocytes by confocal and immunoelectron microscopy and by coprecipitations (immuno- and GST fusion proteins). Cultured podocytes will be used to define signaling from Ga12 to Rho and/or Src kinase pathways. A combination of inhibitors and stable podocyte cell lines expressing active and inactive mutants of Ga12, Rho, and Src will be established to characterize functional effects on the barrier (paracellular flux assays) and changes in structure (by confocal localization of signaling (Ga12, Rho, Src) and slit diaphragm (ZO-t, actin, nephrin)) proteins. In Aim 2, animal models will be developed to characterize these signaling pathways in-vivo. Two approaches will be utilized; A "knock in" of active Ga12 (Q229L) and transgenic podocyte specific expression of Q229La12. A targeting construct for the "knock in" is nearly complete, and the mouse podocin (NPHS2) promoter wil be used for targeting activated Ga12 to the podocyte. Animals will be studied biochemically for evidence of renal disease (proteinuria, creatinine) and morphologically by light and electron microscopy at various ages. Results from studies in cultured podocytes will determine future transgenic models (Rho, Src). These studies will reveal novel insights into regulation of podocyte structure and function. The animal models will extend these findings to in-vivo systems where novel treatment strategies for common podocyte diseases (diabetes and others) can be tested.